On the histogenesis of osseous structures in epithelial tumours. A light and electronmicroscopical study illustrated at the so-called mixed tumour of the mammary gland in bitches (author's transl).

: The osseous areas of 126 canine mixed tumours of the mammary gland were studied by light microscopy. Seven cases were investigated in detail using the electronmicroscop. It is suggested, that these structures develop by enchondral ossification. There ist no indication that myoepithelial tumour cells play a role in formation of osteoid or osseous foci. The cells taking part in enchondral ossification in such tumours cannot be distinguished from cell normally found in enchondral ossification. They derive from the stroma growing into the chondroid matrix. Areas developed by enchondral ossification therefore cannot be considered as tumour tissue in the true sense.